<!DOCTYPE html>

<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>作业</title>

        <style type="text/css">
            .wrapper {
                height: 800px ;
                width: 800px ;
                margin: auto ;
                border: 2px dashed blue ;
                background: url(liuyifei.jpg) left top/200px 200px no-repeat , 
                            url(liuyifei.jpg) right top/200px 200px no-repeat , 
                            url(liuyifei.jpg) left bottom/200px 200px no-repeat ,
                            url(liuyifei.jpg) right bottom/200px 200px no-repeat ,
                            url(liuyifei.jpg) center center/200px 200px no-repeat ;
             }
        </style>

    </head>
    <body>

        <div class="wrapper">
            在这个元素的四个角落使用不同的背景图像。
        </div>
        
    </body>
</html>